Jensen U.S. Pat. No. 5,133,821 and Samuelsen U.S. Pat. No. 4,867,748 disclose dressings having adhesive layers of hydrocolloid-containing materials with upper surfaces protected by covering layers, preferably of elastomeric film, and undersurfaces protected by removable release sheets. The Samuelsen patent suggests that such a contoured dressing may be made by a pressing and molding operation using blanks in which the three layers are pre-laminated together and, following the molding step, the blanks are then die cut in a conventional manner. The Jensen patent discloses a continuous method in which contoured dressings are produced by advancing webs of material through three successive operating stations.
In the first operating station of the Jensen patent, a strip of adhesive material containing hydrocolloids, and supported upon a release web, is contoured between a pair of rollers. According to the patent, the upper contouring roller may be coated with a release agent to prevent it from sticking to the adhesive material but, in a preferred embodiment, a web of silicone-coated release paper is interposed between the contouring roller and the adhesive material. The release paper is sacrificial and is removed from the adhesive layer in a delaminating step following the contouring step. Thereafter, the adhesive surface of each partially-formed dressing is covered by a so-called adhesive carrier layer in a second laminating station, the adhesive carrier layer thereby taking the place of the removed paper layer used in the contouring step. Finally, the second laminate advances from the laminating station to a cutting station where the finished dressings are cut into final shape between a pair of cutting rollers.
The Jensen patent does not elaborate on why it is important that the contouring, laminating and cutting steps be carried out in three successive stations and, in particular, why it is critical that contouring be completed before the adhesive carrier layer is applied to the exposed surface of the adhesive layer. Experience has shown that the sequence is indeed important and that if the adhesive carrier layer (i.e., the backing layer) is a thin elastomeric film, it is not suitable for use as the release web in the contouring station for purposes of preventing the contouring roller from adhering to the adhesive layer. Hence, in a continuous process for making hydrocolloid dressings, the prior art has emphasized the necessity of having successive stations for contouring, laminating, and cutting, with the complexities in equipment and timed operation that such a system inherently require.
Other references revealing the state of the art are U.S. patents to Gross U.S. Pat. No. 4,340,557, Morgan U.S. Pat. No. 4,867,821, Lauritzen U.S. Pat. No. 4,622,089, Eastin U.S. Pat. No. 5,201,976, Tsukamoto et al U.S. Pat. No. 5,006,189, Willhite et al U.S. Pat. No. 4,823,783, Beisang et al U.S. Pat. No. 4,780,168, Trenka U.S. Pat. No. 5,074,944, Wright U.S. Pat. No. 3,824,761 and Volke U.S. Pat. No. 4,963,858.
A main aspect of this invention therefore lies in the discovery, that, contrary to the teachings of the prior art, it is indeed possible to make contoured hydrocolloid wound dressings in an operation in which at least the contouring and cutting steps are combined, and preferably the laminating, contouring and cutting steps are combined, with such steps being performed simultaneously to produce a highly effective product in which a stretchable backing layer covers the contoured adhesive surface of the dressing without wrinkles and deformations. A further aspect of the invention lies in the discovery that such steps may be combined at a single operating station to produce a product free of wrinkles and deformations if the backing layer is restrained against stretching along the general plane of the product being formed, or the simultaneous processing steps are carried out in a manner to avoid such stretching, as the hydrocolloid-containing adhesive material is displaced to form the contoured product.
Avoidance of stretching of the backing material in the plane of the dressing allows the contouring step to be combined with the cutting step and, preferably, with the laminating step, all at a single operating station. The steps taken to avoid such stretching of the backing layer during processing depend on factors such as the stretchability, recoverability and thickness of the backing material selected, the flowability and adhesiveness of the hydrocolloid-containing material, and the temperature at which the operation is performed. In general, it has been found that the backing layer must be able to resist stretching along the plane of the dressing (as exemplified by the plane of the flat release sheet or web) in response to shear forces exerted by the hydrocolloid-containing adhesive material as that material is forced to flow outwardly and/or inwardly under compression. Where the backing material is highly stretchable and would be incapable of resisting such stretching action in response to the outward/inward flow of the adhesive material in a contouring operation, it has been found that stretching of the backing layer may be prevented by removably attaching to it a flexible and substantially non-stretchable reinforcing layer. Ideally, if the stretchable backing layer is a film, then the reinforcing layer may also provide the surface on which the film was originally cast.
Another aspect of the invention lies in the further discovery that the three operations--laminating, contouring and cutting--may be performed simultaneously by the same contouring, laminating and cutting dies. Preferably, such dies are in the form of rollers, although it is possible that the contouring and cutting operations may be performed simultaneously at one station by a pair of reciprocating plates and the laminating operation performed either at the same station or immediately adjacent to it.
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.